US20180257166A1 - Multi-step direct welding of an aluminum-based workpiece to a steel workpiece - Google Patents
Multi-step direct welding of an aluminum-based workpiece to a steel workpiece Download PDFInfo
- Publication number
- US20180257166A1 US20180257166A1 US15/976,163 US201815976163A US2018257166A1 US 20180257166 A1 US20180257166 A1 US 20180257166A1 US 201815976163 A US201815976163 A US 201815976163A US 2018257166 A1 US2018257166 A1 US 2018257166A1
- Authority
- US
- United States
- Prior art keywords
- workpiece
- weld
- aluminum
- steel
- spot welding
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
- B23K11/20—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded of different metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/10—Spot welding; Stitch welding
- B23K11/11—Spot welding
- B23K11/115—Spot welding by means of two electrodes placed opposite one another on both sides of the welded parts
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/18—Dissimilar materials
- B23K2103/20—Ferrous alloys and aluminium or alloys thereof
-
- B23K2203/20—
Definitions
- the technical field of this disclosure relates generally to resistance spot welding and, more particularly, to resistance spot welding a workpiece stack-up that includes an aluminum-based workpiece and a steel workpiece assembled in overlapping fashion relative to one another.
- Resistance spot welding is a process used by a number of industries to join together two or more metal workpieces.
- the automotive industry for example, often uses resistance spot welding to join together pre-fabricated metal workpieces during the manufacture of a vehicle door, hood, trunk lid, or lift gate, among others.
- a number of spot welds are typically formed along a peripheral edge of the metal workpieces or some other bonding region to ensure the part is structurally sound.
- spot welding has typically been practiced to join together certain similarly-composed metal workpieces—such as steel-to-steel and aluminum alloy-to-aluminum alloy—the desire to incorporate lighter weight materials into a vehicle body structure has generated interest in joining steel workpieces to aluminum-based (aluminum or aluminum alloy) workpieces by resistance spot welding.
- Resistance spot welding in general, relies on the resistance to the flow of an electrical current through overlapping metal workpieces and across their faying interface to generate heat.
- a pair of opposed spot welding electrodes are typically clamped at diametrically aligned spots on opposite sides of the workpieces at a predetermined weld site.
- An electrical current is then passed through the metal workpieces from one electrode to the other. Resistance to the flow of this electrical current generates heat within the metal workpieces and at their faying interface.
- the heat generated at the faying interface initiates a molten weld pool extending into the aluminum-based workpiece from the faying interface.
- This molten weld pool wets the adjacent surface of the steel workpiece and, upon cessation of the current flow, solidifies into a weld nugget that forms all or part of a weld joint.
- the aluminum-based workpiece usually contains one or more refractory oxide layers on its surface.
- the oxide layer(s) are typically composed of aluminum oxides, although other oxide compounds may also be present.
- the oxide layer(s) also typically include magnesium oxides.
- the oxide layer(s) present on the aluminum-based workpiece are electrically insulating and mechanically tough.
- the oxide layer(s) have a tendency to remain intact at the faying interface where they can hinder the ability of the molten weld pool to wet the steel workpiece.
- Efforts have been made in the past to remove the oxide layer(s) from the aluminum-based workpiece prior to spot welding. Such removal practices can be unpractical, though, since the oxide layer(s) have the ability to self-heal or regenerate in the presence of oxygen, especially with the application of heat from spot welding operations.
- the steel workpiece and the aluminum-based workpiece also possess different properties that tend to complicate the spot welding process. Specifically, steel has a relatively high melting point ( ⁇ 1500° C.) and relatively high electrical and thermal resistivities, while the aluminum-based material has a relatively low melting point ( ⁇ 600° C.) and relatively low electrical and thermal resistivities. As a result of these physical differences, most of the heat is generated in the steel workpiece during current flow. This heat imbalance sets up a temperature gradient between the steel workpiece (higher temperature) and the aluminum-based workpiece (lower temperature) that initiates rapid melting of the aluminum-based workpiece.
- the combination of the temperature gradient created during current flow and the high thermal conductivity of the aluminum-based workpiece means that, immediately after the electrical current ceases, a situation occurs where heat is not disseminated symmetrically from the weld site. Instead, heat is conducted from the hotter steel workpiece through the aluminum-based workpiece towards the welding electrode in contact with the aluminum-based workpiece, which creates a steep thermal gradient between the steel workpiece and the welding electrode.
- the sustained elevated temperature in the steel workpiece promotes the growth of brittle Fe—Al intermetallic compounds at and along the faying interface.
- the intermetallic compounds tend to form thin reaction layers between the weld nugget and the steel workpiece. These intermetallic layers are generally considered part of the weld joint, if present, in addition to the weld nugget. Having a dispersion of weld nugget defects together with excessive growth of Fe—Al intermetallic compounds along the faying interface tends to reduce the peel strength of the final weld joint.
- a workpiece stack-up that includes at least a steel workpiece and an aluminum-based workpiece can be resistance spot welded—such that a weld joint is formed at a faying interface of the steel and aluminum-based workpieces—by employing a multi-stage spot welding method.
- the multi-stage spot welding is practiced by controlling the passage of electrical current between opposed spot welding electrodes and through the workpiece stack-up to perform multiple stages of weld joint development that include: (1) a molten weld pool growth stage in which a molten weld pool is initiated and grown within the aluminum-based workpiece; (2) a molten weld pool solidification stage in which the molten weld pool is allowed to cool and solidify into a weld nugget that forms all or part of a weld joint; (3) a weld nugget re-melting stage in which at least a portion of the weld nugget is re-melted; (4) a re-melted weld nugget solidification stage in which the re-melted portion of the weld nugget is allowed to cool and solidify; and optionally (5) a metal expulsion stage in which at least part of the re-melted portion of the weld nugget is expelled along the faying interface of the workpieces.
- FIG. 1 is a side elevational view of a workpiece stack-up, which includes a steel workpiece and an aluminum-based workpiece, situated between opposed spot welding electrodes of a weld gun in preparation for spot welding;
- FIG. 2 is a partial magnified view of the workpiece stack-up and the opposed welding electrodes depicted in FIG. 1 ;
- FIG. 3 is a partial cross-sectional view of the workpiece stack-up during part of the multi-stage welding method in which a molten weld pool has been initiated and grown within the aluminum-based workpiece;
- FIG. 4 is a partial cross-sectional view of the workpiece stack-up during part of the multi-stage welding method after the molten weld pool has been allowed to cool and solidify into a weld nugget that forms all or part of a weld joint;
- FIG. 5 is a partial cross-sectional view of the workpiece stack-up during part of the multi-stage welding method in which at least a portion of the weld nugget has been re-melted;
- FIG. 6 is a partial cross-sectional view of the workpiece stack-up after the re-melted portion of the weld nugget has been allowed to cool and solidify;
- FIG. 7 is a perspective view of the workpiece stack-up, from the bottom, in which the steel workpiece is shown in phantom to schematically illustrate the weld bond area of the weld nugget as well as the possible additional weld bond area that may be attained as a result of re-melting at least a portion of the weld nugget during the multi-stage welding method;
- FIG. 8 is a weld schedule depicting a single step constant current that has conventionally been used in spot welding applications
- FIG. 9 is a weld schedule showing one example of the disclosed multi-stage spot welding method.
- FIG. 10 is a weld schedule showing another example of the disclosed multi-stage spot welding method.
- FIG. 11 is a weld schedule showing yet another example of the disclosed multi-stage spot welding method.
- FIG. 12 is a weld schedule showing still another example of the disclosed multi-stage spot welding method.
- FIG. 13 is a weld schedule showing still another example of the disclosed multi-stage spot welding method.
- the resultant thermal gradient established between the workpieces during and just after electrical current flow has a tendency to drive gas porosity and other disparities in the molten weld pool, including the residual oxide defects, towards and along the faying interface, and also contributes to the formation and growth of brittle Fe—Al intermetallic compounds at the faying interface in the form of one or more thin reaction layers on the steel workpiece.
- a multi-stage spot welding method has been devised that counterbalances these challenges and improves the ability to successfully and repeatedly spot weld steel and aluminum-based workpieces together.
- the multi-stage spot welding method invokes control of the electrical current passed between opposed welding electrodes and through the steel and aluminum-based workpieces in order to carry out multiple stages of weld joint development.
- the multiple stages include: (1) a molten weld pool growth stage in which a molten weld pool is initiated and grown within the aluminum-based workpiece; (2) a molten weld pool solidification stage in which the molten weld pool is allowed to cool and solidify into a weld nugget that forms all or part of a weld joint (the weld joint may also include intermetallic compound layers); (3) a weld nugget re-melting stage in which at least a portion of the weld nugget is re-melted; (4) a re-melted weld nugget solidification stage in which the re-melted portion of the weld nugget is allowed to cool and solidify; and optionally (5) a metal expulsion stage in which at least part of the re-melted portion of
- stage 3 The several stages of the disclosed method, in particular the weld nugget re-melting stage (stage 3), function to diminish the adverse effects of, and at least partially eradicate, the weld defects in the weld nugget that are believed to weaken the weld joint.
- the multi-stage spot welding method thus enhances the strength, especially the peel strength, of the ultimately-formed weld joint that gets put into service.
- FIGS. 1-7 illustrate exemplary embodiments of the multi-stage spot welding method as performed on a workpiece stack-up 10 by a weld gun 18 that is mechanically and electrically configured to execute spot welding practices in accordance with a programmed weld schedule.
- the workpiece stack-up 10 includes at least a steel workpiece 12 and an aluminum-based workpiece 14 .
- the workpiece stack-up 10 may include only the steel and aluminum-based workpieces 12 , 14 .
- other metal workpieces may also be included in the stack-up 10 , despite not being shown here, such as an additional steel workpiece or an additional aluminum-based workpiece.
- workpiece and its steel and aluminum-based variations is used broadly in the present disclosure to refer to a sheet metal layer, a casting, an extrusion, or any other piece that is resistance spot weldable, inclusive of any surface layers or coatings, if present.
- the steel workpiece 12 may be coated or uncoated steel.
- Such workpieces include galvanized (zinc-coated) low carbon steel, low carbon bare steel, galvanized advanced high strength steel (AHSS), and hot-stamped boron steel.
- Some specific types of steels that may be used in the steel workpiece 12 are interstitial-free (IF) steel, dual-phase (DP) steel, transformation-induced plasticity (TRIP) steel, high-strength low alloy (HSLA) steel, and press-hardened steel (PHS).
- IF interstitial-free
- DP dual-phase
- TRIP transformation-induced plasticity
- HSLA high-strength low alloy
- PHS press-hardened steel
- the aluminum-based workpiece 14 it may coated or uncoated aluminum or aluminum alloy.
- Aluminum alloys contain 85 wt.
- % or more aluminum such as 5XXX, 6XXX, and 7XXX series aluminum alloys—and can be employed in a variety of tempers.
- aluminum alloys that may be employed include an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy, or an aluminum-zinc alloy, any of which may be coated with zinc or a conversion coating to improve adhesive bond performance, if desired.
- Some specific aluminum alloys that may be used in the aluminum-based workpiece 14 are AA5754 and AA5182 aluminum-magnesium alloy, AA6111 and AA6022 aluminum-magnesium-silicon alloy, and AA7003 and 7055 aluminum-zinc alloy.
- the steel and aluminum-based workpieces 12 , 14 are assembled in overlapping fashion for resistance spot welding at a predetermined weld site 16 by the weld gun 18 .
- the steel workpiece 12 includes a faying surface 20 and an exterior surface 22 .
- the aluminum-based workpiece 14 includes a faying surface 24 and an exterior surface 26 .
- the faying surfaces 20 , 24 of the two workpieces 12 , 14 overlap and contact one another to provide a faying interface 28 at the weld site 16 .
- the faying interface 28 encompasses instances of direct contact between the faying surfaces 20 , 24 of the workpieces 12 , 14 as well as instances of indirect contact in which the faying surfaces 20 , 24 are not touching but are in close enough proximity to each another—such as when a thin layer of adhesive, sealer, or some other intermediate material is present—that resistance spot welding can still be practiced.
- the exterior surfaces 22 , 26 of the steel and aluminum-based workpieces 12 , 14 on the other hand, generally face away from each other in opposite directions.
- Each of the steel and aluminum-based workpieces 12 , 14 preferably has a thickness 120 , 140 that ranges from about 0.3 mm to about 6.0 mm, and more preferably from about 0.5 mm to about 3.0 mm, at least at the weld site 16 .
- the thicknesses 120 , 140 of the workpieces 12 , 14 can be the same but do not have to be.
- the weld gun 18 is shown schematically in FIG. 1 and is one part of a larger automated welding operation within a manufacturing setting.
- the weld gun 18 may be mounted on a robot positioned in the vicinity of a conveyor or other transport device that is set up to deliver the workpiece stack-up 10 (as well as others like it and others unlike it) to the weld gun 18 .
- the robot may be constructed to move the weld gun 18 along the workpiece stack-up 10 , once delivered, so that a rapid succession of spot welds can be formed at many different weld sites 16 .
- the weld gun 18 may also be a stationary pedestal-type weld gun in which the workpiece stack-up 10 is manipulated and moved relative to the weld gun 18 to enable the formation of multiple spot welds at different weld sites 16 around the stack-up 10 .
- the weld gun 18 is, of course, meant to represent other types and arrangements of weld guns not specifically mentioned or described here so long as they are capable of spot welding the workpiece stack-up 10 according to the prescribed multi-step spot welding method.
- the weld gun 18 includes a first gun arm 30 and a second gun arm 32 that are mechanically and electrically configured to repeatedly form spot welds in accordance with a defined weld schedule.
- the first gun arm 30 has a first electrode holder 34 that retains a first spot welding electrode 36
- the second gun arm 32 has a second electrode holder 38 that retains a second spot welding electrode 40 .
- the first and second spot welding electrodes 36 , 40 are each preferably formed from an electrically conductive material such as copper alloy.
- an electrically conductive material such as copper alloy.
- ZrCu zirconium copper alloy
- Copper alloys that meet this constituent composition and are designated C15000 are preferred.
- Other copper alloy compositions that possess suitable mechanical and electrical conductive properties may also be employed.
- the first spot welding electrode 36 includes a first weld face 42 and the second spot welding electrode 40 includes a second weld face 44 .
- the weld faces 42 , 44 of the first and second spot welding electrodes 36 , 40 are the portions of the electrodes 36 , 40 that are pressed against, and impressed into, opposite sides of the workpiece stack-up 10 during a spot welding event, which, here, are the exterior surfaces 22 , 26 of the workpieces 12 , 14 .
- a broad range of electrode weld face designs may be implemented for each spot welding electrode 36 , 40 .
- Each of the weld faces 42 , 44 may be flat or domed, and may further include surface features (e.g., surface roughness, ringed features, a plateau, etc.) as described, for example, in U.S. Pat. Nos. 6,861,609, 8,222,560, 8,274,010, 8,436,269, and 8,525,066, and U.S. Pat. Pub. No. 2009/0255908.
- a mechanism for cooling the electrodes 36 , 40 with water is also typically incorporated into the gun arms 30 , 32 and the electrode holders 34 , 38 to manage the temperatures of the spot welding electrodes 36 , 40 .
- the first and second spot welding electrodes 36 , 40 can share the same general configuration or a different one.
- the weld face 42 , 44 of each spot welding electrode 36 , 40 may have a diameter between 5 mm and 20 mm, or more narrowly between 8 mm and 12 mm, and a radius of curvature between 5 mm and flat, or more narrowly between 20 mm and 50 mm.
- Each weld face 42 , 44 may further include a series of radially-spaced ringed ridges that project outwardly from a base surface of the weld face 42 , 44 .
- Such an electrode weld face design is quite useful when pressed into contact against an aluminum-based workpiece since the ringed ridges function to stretch and breakdown the surface oxide layer(s) on the aluminum-based workpiece to establish better electrical and mechanical contact at the electrode/workpiece junction.
- the same electrode weld face design is also able to function effectively when pressed into contact against a steel workpiece primarily due to the radius of curvature.
- the ringed ridges have very little effect on the commutation of current through a steel workpiece and, in fact, are quickly deformed by the stresses associated with being pressed against a steel workpiece during spot welding.
- conventional steel and aluminum-based spot welding electrodes known to skilled artisans may be used as the first and second spot welding electrodes 36 , 40 , respectively, including ball-nose, domed, and flat spot welding electrodes.
- the welding gun arms 30 , 32 are operable during spot welding to press the weld faces 42 , 44 of the spot welding electrodes 36 , 40 against opposite sides of the workpiece stack-up 10 .
- the opposite sides of the workpiece stack-up 10 are the oppositely-facing exterior surfaces 22 , 26 of the overlapping steel and aluminum-based workpieces 12 , 14 .
- the first and second gun arms 30 , 32 have approximately orthogonal longitudinal axes, and the first gun arm 30 is moveable along its longitudinal axis towards the second gun arm 32 by an actuator 46 such as an air cylinder or a servo motor.
- An actuator control 48 may cause compressed air to be delivered to the actuator 46 , if the actuator 46 is an air cylinder, or it may cause current/voltage to be delivered to the actuator 46 , if the actuator 46 is a servo motor, to move the first gun arm 30 as intended to press the weld faces 42 , 44 against opposite sides of the workpiece stack-up 10 (surfaces 22 , 26 ) and to apply the desired clamping force.
- the first and second weld faces 42 , 44 are typically pressed against their respective exterior surfaces 22 , 26 in diametric alignment with one another at the weld site 16 .
- the weld gun 18 is also configured to pass electrical current between the first and second spot welding electrodes 36 , 40 —and through the workpiece stack-up 10 at the weld site 16 —when the weld faces 42 , 44 of the electrodes 36 , 40 are pressed against the opposite sides of the stack-up 10 .
- Electrical current can be delivered to the weld gun 18 from a controllable power supply 50 .
- the power supply 50 is preferably a medium-frequency DC (MFDC) power supply that electrically communicates with the spot welding electrodes 36 , 40 .
- a MFDC power supply generally includes a transformer and a rectifier.
- the transformer “steps down” an input AC voltage—usually about 1000 Hz—to generate a lower-voltage, higher-amperage AC current which is then fed to the rectifier where a collection of semiconductor diodes converts the supplied AC current into a DC current.
- a power supply component is commercially available from a number of suppliers including ARO Welding Technologies (US headquarters in Chesterfield Township, Mich.) and Bosch Rexroth (US headquarters in Charlotte, N.C.).
- the power supply 50 is controlled by a weld controller 52 in accordance with a programmed weld schedule.
- the weld controller 52 which cooperates with the actuator control 48 (by means not shown), interfaces with the power supply 50 and sets the applied current level, duration, and current type (constant, pulsed, etc.) of electrical current being passed between the spot welding electrodes 36 , 40 in order to carry out the multi-stage spot welding method.
- the weld controller 52 instructs the power supply 50 to deliver electrical current such that the various stages of weld joint development called for in the multi-stage spot welding method are accomplished.
- the stages of the multi-stage spot welding method include (1) the molten weld pool growth stage, (2) the molten weld pool solidification stage, (3) the weld nugget re-melting stage, (4) the re-melted weld nugget solidification stage, and optionally (5) the metal expulsion stage, each of which will be explained in more detail below.
- the multi-stage spot welding method including its various stages of weld joint development, is illustrated in general schematic fashion.
- the workpiece stack-up 10 is located between the first and second spot welding electrodes 36 , 40 so that the weld site 16 is generally aligned with the opposed weld faces 42 , 44 .
- the workpiece stack-up 10 may be brought to such a location, as is often the case when the gun arms 30 , 32 are part of a stationary pedestal welder, or the gun arms 30 , 32 may be robotically moved to locate the electrodes 36 , 40 relative to the weld site 16 .
- the first and second gun arms 30 , 32 converge relative to one another to contact and press the weld faces 42 , 44 of the first and second spot welding electrodes 36 , 40 against opposite sides of the stack-up 10 at the weld site 16 , which, in this embodiment, are the oppositely-facing exterior surfaces 22 , 26 of the steel and aluminum-based workpieces 12 , 14 , as shown in FIG. 3 .
- the first and second weld faces 42 , 44 impress into their respective opposite side surfaces of the stack-up 10 .
- the resultant indentations originated by the opposed weld faces 42 , 44 are referred to here as a first contact patch 54 and a second contact patch 56 .
- the molten weld pool growth stage is commenced once the spot welding electrodes 36 , 40 are pressed against the workpiece stack-up 10 at the weld site 16 .
- a molten weld pool 58 is initiated and grown within the aluminum-based workpiece 14 , as schematically depicted in FIG. 3 .
- the molten weld pool 58 extends from the faying interface 28 of the workpieces 12 , 14 into the aluminum-based workpiece 14 . And it is composed predominantly of molten aluminum-based material from the aluminum-based workpiece 14 since the steel workpiece 12 typically does not melt.
- the molten weld pool 58 may penetrate a distance into the aluminum-based workpiece 14 that ranges from 20% to 100% (i.e., all the way through the aluminum-based workpiece 14 ) of the thickness 140 of the aluminum-based workpiece 14 at the weld site 16 .
- the thickness 140 of the aluminum-based workpiece 14 at the weld site 16 is typically less than the thickness outside of the weld site 16 due to the indentation of the second contact patch 56 on the workpiece stack-up 10 .
- the portion of the molten weld pool 58 adjacent to the faying interface 28 consequently, wets the faying surface 20 of the steel workpiece 12 .
- the molten weld pool 58 is initiated and grown by passing electrical current between the spot welding electrodes 36 , 40 and through the workpieces 12 , 14 and across their faying interface 28 for a first period of time. Resistance to the flow of the electrical current through the workpieces 12 , 14 and across the faying interface 28 generates heat and initially heats up the steel workpiece 12 more quickly than the aluminum-based workpiece 14 . The generated heat eventually initiates the molten weld pool 58 and then continues to grow the molten weld pool 58 to its desired size.
- the molten weld pool 58 initiates quickly and rapidly grows and penetrates into the aluminum-based workpiece 14 .
- the electrical current density decreases and the molten weld pool 58 grows more laterally in the vicinity of the faying interface 28 .
- the level of the applied electrical current and the duration of the first period of time depend on several factors.
- the main factors that influence the electrical current level and duration are the thicknesses 120 , 140 of the steel and aluminum-based workpieces 12 , 14 at the weld site 16 and the exact compositions of the workpieces 12 , 14 .
- the electrical current passed during the weld pool growth stage is a constant direct current (DC) that has a current level between 4 kA and 40 kA and the duration of electrical current flow is between 50 ms and 500 ms.
- the electrical current alternatively, may be pulsed, in which over the course of the first period of time, the passing electrical current is a plurality of current pulses.
- Each of the current pulses may last from 10 ms to 200 ms and have a peak current level between 10 kA and 50 kA, with periods of zero current flow lasting from 1 ms to 100 ms between pulses.
- Other current levels and durations of the first period of time may of course be employed and, in fact, skilled artisans will know and understand how to adjust these parameters accordingly in order to satisfy the molten weld pool growth stage.
- the molten weld pool solidification stage is carried out.
- the molten weld pool 58 is allowed to cool and solidify into a weld nugget 60 that forms all or part of a weld joint 62 , as illustrated in FIG. 4 . Cooling and solidification of the molten weld pool 58 can be realized over a second period of time in one of two ways. First, passage of electrical current between the first and second spot welding electrodes 36 , 40 can be ceased.
- electrical current can be passed between the first and second spot welding electrodes 36 , 40 at a reduced level that would be unable to maintain the molten state of the weld pool 58 , thus allowing the molten weld pool 58 to cool and solidify, albeit at a slower rate than ceasing electrical current flow entirely.
- the duration of the second period of time and the reduced current level may vary depending on the thicknesses 120 , 140 of the workpieces 12 , 14 at the weld site 16 and the actual compositions of the workpieces 12 , 14 . Passing an electrical current below 5 kA, or ceasing current, for between 50 ms and 1000 ms is usually sufficient to solidify the molten weld pool 58 into the weld nugget 60 .
- the weld nugget 60 extends a distance from the faying interface 28 into the aluminum-based workpiece 14 to a penetration depth 64 .
- the penetration depth 64 of the weld nugget 60 may range from 20% to 100% (i.e., all the way through the aluminum-based workpiece 14 ) of the thickness 140 of the aluminum-based workpiece 14 at the weld site 16 .
- the thickness 140 of the aluminum-based workpiece 14 at the weld site 16 is typically less than the thickness outside of the weld site 16 due to the indentation of the second contact patch 56 on the workpiece stack-up 10 .
- the weld nugget 60 defines a weld bond area 66 , as shown in FIG.
- the weld bond area 66 is preferably at least 4( ⁇ )(t) in which “t” is the thickness 140 of the aluminum-based workpiece 14 in millimeters at the weld site 16 prior to origination of the second contact patch 56 .
- the thickness “t” of the aluminum-based workpiece 14 is the original thickness of the workpiece 14 as measured prior to indentation of the weld face 44 of the second spot welding electrode 40 .
- the weld bond area 66 can be varied as desired by managing the size of the molten weld pool 58 grown in the molten weld pool growth stage.
- the weld nugget 60 may include weld defects dispersed at and along the faying interface 28 within the weld bond area 66 . These defects—which can include gas porosity, shrinkage voids, micro-cracking, and surface oxide residue—are believed to be swept towards the faying interface 28 during solidification of the molten weld pool 58 where they have a tendency weaken the strength of the weld joint 62 , in particular the peel strength, as previously explained.
- the weld joint 62 may also include, in addition to the weld nugget 60 , one or more thin reaction layers of Fe—Al intermetallic compounds (not shown) on the steel workpiece 12 and adjacent to the faying interface 28 , as previously indicated.
- the one or more layers of Fe—Al intermetallic compounds may include intermetallics such as FeAl 3 , Fe 2 Al 5 , as well others, and their combined thickness typically ranges from 1 ⁇ m to 10 ⁇ m.
- the hard and brittle nature of the Fe—Al intermetallic compounds is also thought to negatively affect the strength of the overall weld joint 62 .
- the weld nugget re-melting stage is performed. During the weld nugget re-melting stage, at least a portion 68 of the weld nugget 60 is re-melted, as depicted in FIG. 5 .
- the re-melted portion 68 of the weld nugget 60 preferably includes at least part of the weld bond area 66 that was established during the molten weld pool solidification stage. It also typically does not extend all the way to the penetration depth 64 of the weld nugget 60 .
- the shallower penetration of the re-melted portion 68 occurs because at the time of the weld nugget re-melting stage, the weld face 44 of the second spot welding electrode 40 has indented further into the workpiece stack-up 10 , and the second contact patch 56 has correspondingly increased in size, meaning that electrical current is passed between the spot welding electrodes 36 , 40 over a broader area, which has the effect of promoting re-melting closer to the faying interface 28 with less penetration into the aluminum-based workpiece 14 .
- the re-melted portion 68 of the weld nugget 60 may be entirely confined within the weld bond area 66 or it may encompass the entire weld bond area 66 and actually combine with freshly melted material from the aluminum-based workpiece 14 outside of, and adjacent to, the weld bond area 66 to established an enlarged weld bond area 70 ( FIG. 7 ).
- the area of the enlarged weld bond area 70 if created, may be up to 50% greater than the weld bond area 66 of the weld nugget 60 before re-melting.
- the weld nugget 60 is at least partially re-melted by passing electrical current between the spot welding electrodes 36 , 40 and through the workpieces 12 , 14 for a third period of time following the molten weld pool solidification stage. Passage of electrical current, here, is generally done at a higher level than in the molten weld pool growth stage since the weld face 44 of the second spot welding electrode 40 is further impressed into the workpiece stack-up 10 and the faying interface 28 is less liable to generate heat within the weld site 16 since the weld joint 62 is more electrically conductive than the distinct, unjoined faying surfaces 20 , 24 of the workpieces 12 , 14 .
- the level of the applied electrical current and the duration of the third period of time depend on the thicknesses 120 , 140 of the steel and aluminum-based workpieces 12 , 14 at the weld site 16 and the exact compositions of the workpieces 12 , 14 .
- the electrical current passed during the weld nugget re-melting stage may be a constant direct current (DC) that has a current level between 10 kA and 50 kA and the duration of electrical current flow may be between 100 ms and 2000 ms.
- the electrical current can also be pulsed.
- the electrical current delivered during the weld nugget re-melting stage is preferably in the form of current pulses that may or may not increase in applied current level over the course of the third period of time.
- the passing electrical current is a plurality of current pulses delivered over the third period of time.
- Each current pulse may last from 10 ms to 200 ms and have a peak current level between, for example, 15 kA and 50 kA, with periods of zero current flow lasting from, for example, 1 ms to 100 ms between pulses.
- the current pulses can be said to increase in applied current level when at least 75% of the current pulses, and preferably 100%, attain a peak current level that is greater than the peak current level of the immediately preceding current pulse.
- the use of current pulses may be practiced in the weld nugget re-melting stage for several reasons. Most notably, the use of current pulses helps prevent excessive penetration of the re-melted portion 68 of the weld nugget 60 by keeping the electrode/workpiece cool, which also has the benefit of preserving the operational lifetime of the second spot welding electrode 40 .
- the re-melting of the weld nugget 60 is believed to positively impact the strength, including the peel strength, of the ultimately-formed weld joint 62 that is placed into service. Without being bound by theory, it is believed that re-melting the weld nugget 60 , especially the weld bond area 66 at the faying interface 28 , cleans out the various weld defects that get driven to and along the faying interface 28 during solidification of the molten weld pool 58 , thus improving the ability of the weld nugget 60 to bond with the faying surface 20 of the steel workpiece 12 .
- the creation of the re-melted portion 68 is thought to consolidate entrained gas porosity near the center of the weld nugget 62 , and possibly evolve some gas from the re-melted portion 68 , while thermal expansion and contraction of the weld nugget 60 during re-melting is thought to break up and disperse residual oxides and micro-cracks that may be present at the weld bond area 66 or in the vicinity.
- the re-melted weld nugget solidification stage is performed.
- the re-melted portion 68 of the weld nugget 60 (as well as any newly melted material of the aluminum-based workpiece 14 outside of the original weld bond area 66 ) is allowed to cool and solidify, as shown in FIG. 6 , preferably with the first and second spot welding electrodes 36 , 40 still pressed against the workpiece stack-up 10 .
- the re-solidified portion 72 of the weld nugget 60 which is derived from the re-melted portion 68 , is depicted here as a distinct part of the weld nugget 60 although, in actual practice, the re-solidified portion 72 may not be easily distinguishable from the part(s) of the weld nugget 60 (if any) that do not undergo re-melting and re-solidification. And, as alluded to above, the re-solidified portion 72 of the weld nugget 60 is believed to contain less weld defects at or near the faying interface 28 than would otherwise be present had the weld nugget re-melting stage not been practiced. To be sure, it is not uncommon for workpiece stack-ups that have undergone the multi-stage spot welding method to have peel strengths of at least 100% greater than the same workpiece stack-ups that have been spot welded with a conventional single-step constant current.
- the multi-stage spot welding method set forth above may also include an optional metal expulsion stage during or after the weld nugget re-melting stage but prior to the re-melted weld nugget solidification stage.
- an optional metal expulsion stage during or after the weld nugget re-melting stage but prior to the re-melted weld nugget solidification stage.
- the metal expulsion stage at least part of the re-melted portion 68 of the weld nugget 60 is heated to the extent that the hydraulic seal established at the weld site 16 is broken, resulting in the faying surfaces 20 , 24 of the steel and aluminum-based workpieces 12 , 14 being pushed apart briefly (as well as the first and second spot welding electrodes 36 , 40 ).
- the re-melted portion 68 of the weld nugget 60 and possibly some of the newly melted material of the aluminum-based workpiece 14 outside of the original weld bond area 66 , if present, expels or spatters laterally along the faying interface 28 outside of the weld bond area 66 at this time until the workpieces eventually collapse 12 , 14 due to the loss of molten material and the applied pressure of the first and second spot welding electrodes 36 , 40 . It is believed that such metal expulsion, if practiced, helps further clean the weld nugget 60 of weld defects by physically expelling the defects outside of the weld bond area 66 (or the enlarged weld bond area 70 if applicable).
- the heating of the re-melted portion 68 is preferably controlled so that the thickness 140 of the aluminum-based workpiece 14 at the weld site 16 is not reduced to less than 50% of its original thickness, which is measured prior to indentation of the weld face 44 of the second spot welding electrode 40 , as a result of the metal expulsion stage.
- the metal expulsion stage can be accomplished by passing electrical current between the spot welding electrodes 36 , 40 and through the workpieces 12 , 14 in one of two ways.
- the third period of time can be set so that passage of electrical current during the weld nugget re-melting stage continues and ultimately causes metal expulsion at the end of the third period of time.
- the weld nugget re-melting stage and the metal expulsion stage can thus overlap.
- the third period of time typically lasts for 100 ms or greater, although shorter and longer periods are certainly possible depending on the thicknesses 120 , 140 and compositions of the workpieces 12 , 14 .
- electrical current can be passed for a fourth period of time, after the third period of time associated with the weld nugget re-melting stage, during which the electrical current is raised to a higher level than the electrical current passed during the third period of time.
- a direct current may be passed that has a constant current level between 20 kA and 50 kA and the duration of electrical current flow over the fourth period of time may be between 20 ms and 200 ms.
- the first and second spot welding electrodes 36 , 40 are retracted from their respective contact patches 54 , 56 .
- the workpiece stack-up 10 is then successively located relative to the weld gun 18 at other weld sites 16 , and the multi-stage spot welding process is repeated at those sites 16 , or the workpiece stack-up 10 is moved away from the weld gun 18 to make way for another stack-up.
- the above-described multi-stage spot welding method can thus be carried out many times at different weld sites on the same workpiece stack-up as well as different workpiece stack-ups in a manufacturing setting to successfully, consistently, and reliably form weld joints between a steel workpiece and an aluminum-based workpiece.
- the weld schedule of a conventional spot welding method that employs a single step constant electrical current to weld a 1.2-mm 6022 aluminum alloy workpiece to a 1.0-mm hot-dip galvanized low carbon steel workpiece is also illustrated in FIG. 8 for comparative purposes.
- electrical current is passed between the spot welding electrodes and through the workpiece stack-up at a constant current level (after a rapid initial ramp up) of 16 kA for 500 ms under 800 lb of force.
- a constant current level after a rapid initial ramp up
- spot weld joints are formed by controlling passage of electrical current between the spot welding electrodes and through the workpiece stack-ups in order to carry out, in order, a molten weld pool growth stage, a molten weld pool solidification stage, a weld nugget re-melting stage, and a re-melted weld nugget solidification stage.
- a molten weld pool growth stage a molten weld pool solidification stage
- a weld nugget re-melting stage a re-melted weld nugget solidification stage.
- Each of the examples moreover, employs an optional metal expulsion stage before the re-melted weld nugget solidification stage.
- a 1.2-mm 6022 aluminum alloy workpiece was spot welded to a 1.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 800 lb of force applied by the spot welding electrodes.
- the weld schedule is depicted in FIG. 9 .
- electrical current at a constant level of 17 kA was first passed through the workpieces for a first period of 125 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece.
- passage of electrical current was ceased, i.e., dropped to 0 kA, for a second period of 500 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces.
- Electrical current was then re-started and passed through the workpieces to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface of the workpieces.
- the electrical current passed at that time had a constant current level of 25 kA and was maintained for a third period of 200 ms. After the third period of time, passage of electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget.
- a 1.2-mm 6022 aluminum alloy workpiece was spot welded to a 1.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 700 lb of force applied by the spot welding electrodes.
- electrical current at a constant current level of 15 kA was passed through the workpieces for a first period of 300 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece.
- passage of electrical current was ceased for a second period of 500 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces.
- Electrical current was then passed in the form of seven current pulses to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface of the workpieces.
- the seven current pulses increased in applied current level in the range of 16 kA to 20.5 kA over a third period of approximately 860 ms.
- each current pulse lasted for 100 ms while increasing in current level, then dropped to 0 kA for a period of 25 ms between pulses, and the peak current levels of each pulse increased from its immediately succeeding pulse (16.5 kA ⁇ 17.2 kA ⁇ 17.8 kA ⁇ 18.5 kA ⁇ 19.1 kA ⁇ 19.8 kA ⁇ 20.4 kA).
- passage of the electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget.
- a 2.0-mm 6022 aluminum alloy workpiece was spot welded to a 1.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 800 lb of force applied by the spot welding electrodes.
- electrical current at a constant current level of 17 kA was passed through the workpieces for a first period of 125 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece.
- passage of electrical current was ceased for a second period of 500 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces.
- Electrical current was then passed in the form of twenty seven current pulses over a third period of approximately 960 ms to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface.
- Each current pulse reached a current level of 37 kA and maintained that level for 12 ms before dropping to 0 kA for a period of 24 ms between pulses.
- passage of the electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget.
- a 1.2-mm 6022 aluminum alloy workpiece was spot welded to a 2.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 600 lb of force applied by the spot welding electrodes.
- electrical current at a constant level of 13 kA was passed through the workpieces for a first period of 250 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece.
- each current pulse reached a current level of 14 kA and maintained that level for 100 ms before dropping to 0 kA for a period of 15 ms between pulses.
- passage of the electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget.
- a 2.0-mm 6022 aluminum alloy workpiece was spot welded to a 2.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 1200 lb of force applied by the spot welding electrodes.
- electrical current was passed in the form of 20 current pulses over a first period of approximately 400 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece.
- Each current pulse reached a current level of 20 kA and maintained that level for 16 ms before dropping to 0 kA for a period of 4 ms between pulses.
- passage of electrical current was ceased for a second period of 1000 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces.
- Electrical current was then passed in the form of twelve current pulses over a third period of approximately 480 ms to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface.
- Each current pulse reached a current level of 38 kA and maintained that level for 16 ms before dropping to 0 kA for a period of 25 ms between pulses.
- passage of the electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget.
- the following table compares the peel strengths of the conventional single-step constant electrical current welding method ( FIG. 8 ) to the five exemplary multi-step spot welding methods ( FIGS. 9-13 ).
- Weld joint peel strength is noteworthy property for weld joints. This is especially true for weld joints used in conjunction with a structural adhesive since adhesives generally provide shear strength, but perform poorly in peel.
- the peel strengths reported here were measured with T-peel samples. The T-peel samples were obtained by first bending coupons (5 in. by 1.5 in.) into an L-shape. The short legs of two L-shape coupons were then mated and a weld joint was formed according to the above detailed spot welding methods between the mating surfaces.
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Resistance Welding (AREA)
Abstract
Description
- This application is a continuation of U.S. application Ser. No. 14/464,476, filed on Aug. 20, 2014 and published as U.S. Pub. No. 2015/0053655, which in turn claims the benefit of U.S. Provisional Application No. 61/869,281 filed on Aug. 23, 2013. The entire contents of each of the aforementioned applications are hereby incorporated by reference.
- The technical field of this disclosure relates generally to resistance spot welding and, more particularly, to resistance spot welding a workpiece stack-up that includes an aluminum-based workpiece and a steel workpiece assembled in overlapping fashion relative to one another.
- Resistance spot welding is a process used by a number of industries to join together two or more metal workpieces. The automotive industry, for example, often uses resistance spot welding to join together pre-fabricated metal workpieces during the manufacture of a vehicle door, hood, trunk lid, or lift gate, among others. A number of spot welds are typically formed along a peripheral edge of the metal workpieces or some other bonding region to ensure the part is structurally sound. While spot welding has typically been practiced to join together certain similarly-composed metal workpieces—such as steel-to-steel and aluminum alloy-to-aluminum alloy—the desire to incorporate lighter weight materials into a vehicle body structure has generated interest in joining steel workpieces to aluminum-based (aluminum or aluminum alloy) workpieces by resistance spot welding. In particular, the ability to resistance spot weld workpiece stack-ups containing different workpiece combinations (e.g., steel/steel, aluminum-based/steel, and aluminum-based/aluminum-based) with one piece of equipment would promote production flexibility and reduce manufacturing costs.
- Resistance spot welding, in general, relies on the resistance to the flow of an electrical current through overlapping metal workpieces and across their faying interface to generate heat. To carry out such a welding process, a pair of opposed spot welding electrodes are typically clamped at diametrically aligned spots on opposite sides of the workpieces at a predetermined weld site. An electrical current is then passed through the metal workpieces from one electrode to the other. Resistance to the flow of this electrical current generates heat within the metal workpieces and at their faying interface. When the metal workpieces being spot welded together are a steel workpiece and an aluminum-based workpiece, the heat generated at the faying interface initiates a molten weld pool extending into the aluminum-based workpiece from the faying interface. This molten weld pool wets the adjacent surface of the steel workpiece and, upon cessation of the current flow, solidifies into a weld nugget that forms all or part of a weld joint.
- In practice, however, spot welding a steel workpiece to an aluminum-based workpiece is challenging since a number of characteristics of those two metals can adversely affect the strength—most notably the peel strength—of the weld joint. For one, the aluminum-based workpiece usually contains one or more refractory oxide layers on its surface. The oxide layer(s) are typically composed of aluminum oxides, although other oxide compounds may also be present. For example, in the case of magnesium-containing aluminum alloys, the oxide layer(s) also typically include magnesium oxides. The oxide layer(s) present on the aluminum-based workpiece are electrically insulating and mechanically tough. As a result of these physical properties, the oxide layer(s) have a tendency to remain intact at the faying interface where they can hinder the ability of the molten weld pool to wet the steel workpiece. Efforts have been made in the past to remove the oxide layer(s) from the aluminum-based workpiece prior to spot welding. Such removal practices can be unpractical, though, since the oxide layer(s) have the ability to self-heal or regenerate in the presence of oxygen, especially with the application of heat from spot welding operations.
- The steel workpiece and the aluminum-based workpiece also possess different properties that tend to complicate the spot welding process. Specifically, steel has a relatively high melting point (˜1500° C.) and relatively high electrical and thermal resistivities, while the aluminum-based material has a relatively low melting point (˜600° C.) and relatively low electrical and thermal resistivities. As a result of these physical differences, most of the heat is generated in the steel workpiece during current flow. This heat imbalance sets up a temperature gradient between the steel workpiece (higher temperature) and the aluminum-based workpiece (lower temperature) that initiates rapid melting of the aluminum-based workpiece. The combination of the temperature gradient created during current flow and the high thermal conductivity of the aluminum-based workpiece means that, immediately after the electrical current ceases, a situation occurs where heat is not disseminated symmetrically from the weld site. Instead, heat is conducted from the hotter steel workpiece through the aluminum-based workpiece towards the welding electrode in contact with the aluminum-based workpiece, which creates a steep thermal gradient between the steel workpiece and the welding electrode.
- The development of a steep thermal gradient between the steel workpiece and the welding electrode in contact with the aluminum-based workpiece is believed to weaken the integrity of the resultant weld joint in two primary ways. First, because the steel workpiece retains heat for a longer duration than the aluminum-based workpiece after the electrical current has ceased, the molten weld pool solidifies directionally, starting from the region nearest the colder welding electrode (often water cooled) associated with the aluminum-based workpiece and propagating towards the faying interface. A solidification front of this kind tends to sweep or drive defects—such as gas porosity, shrinkage voids, micro-cracking, and surface oxide residue—towards and along the faying interface within the weld nugget. Second, the sustained elevated temperature in the steel workpiece promotes the growth of brittle Fe—Al intermetallic compounds at and along the faying interface. The intermetallic compounds tend to form thin reaction layers between the weld nugget and the steel workpiece. These intermetallic layers are generally considered part of the weld joint, if present, in addition to the weld nugget. Having a dispersion of weld nugget defects together with excessive growth of Fe—Al intermetallic compounds along the faying interface tends to reduce the peel strength of the final weld joint.
- In light of the aforementioned challenges, previous efforts to spot weld a steel workpiece and an aluminum-based workpiece have employed a weld schedule that specifies higher currents, longer weld times, or both (as compared to spot welding steel-to-steel), in order to try and obtain a reasonable weld bond area. Such efforts have been largely unsuccessful in a manufacturing setting and have a tendency to damage the welding electrodes. Given that previous spot welding efforts have not been particularly successful, mechanical processes such as self-piercing rivets and flow-drill screws have predominantly been used instead. Both self-piercing rivets and flow-drill screws are considerably slower and have high consumable costs as compared to spot welding. They also add weight to the vehicle body structure which at some point can begin to counteract the weight savings attained through the use of aluminum-based workpieces in the first place. Advancements in spot welding that would make the process more capable of joining steel and aluminum-based workpieces would thus be a welcome addition to the art.
- A workpiece stack-up that includes at least a steel workpiece and an aluminum-based workpiece can be resistance spot welded—such that a weld joint is formed at a faying interface of the steel and aluminum-based workpieces—by employing a multi-stage spot welding method. The multi-stage spot welding is practiced by controlling the passage of electrical current between opposed spot welding electrodes and through the workpiece stack-up to perform multiple stages of weld joint development that include: (1) a molten weld pool growth stage in which a molten weld pool is initiated and grown within the aluminum-based workpiece; (2) a molten weld pool solidification stage in which the molten weld pool is allowed to cool and solidify into a weld nugget that forms all or part of a weld joint; (3) a weld nugget re-melting stage in which at least a portion of the weld nugget is re-melted; (4) a re-melted weld nugget solidification stage in which the re-melted portion of the weld nugget is allowed to cool and solidify; and optionally (5) a metal expulsion stage in which at least part of the re-melted portion of the weld nugget is expelled along the faying interface of the workpieces.
-
FIG. 1 is a side elevational view of a workpiece stack-up, which includes a steel workpiece and an aluminum-based workpiece, situated between opposed spot welding electrodes of a weld gun in preparation for spot welding; -
FIG. 2 is a partial magnified view of the workpiece stack-up and the opposed welding electrodes depicted inFIG. 1 ; -
FIG. 3 is a partial cross-sectional view of the workpiece stack-up during part of the multi-stage welding method in which a molten weld pool has been initiated and grown within the aluminum-based workpiece; -
FIG. 4 is a partial cross-sectional view of the workpiece stack-up during part of the multi-stage welding method after the molten weld pool has been allowed to cool and solidify into a weld nugget that forms all or part of a weld joint; -
FIG. 5 is a partial cross-sectional view of the workpiece stack-up during part of the multi-stage welding method in which at least a portion of the weld nugget has been re-melted; -
FIG. 6 is a partial cross-sectional view of the workpiece stack-up after the re-melted portion of the weld nugget has been allowed to cool and solidify; -
FIG. 7 is a perspective view of the workpiece stack-up, from the bottom, in which the steel workpiece is shown in phantom to schematically illustrate the weld bond area of the weld nugget as well as the possible additional weld bond area that may be attained as a result of re-melting at least a portion of the weld nugget during the multi-stage welding method; -
FIG. 8 is a weld schedule depicting a single step constant current that has conventionally been used in spot welding applications; -
FIG. 9 is a weld schedule showing one example of the disclosed multi-stage spot welding method; -
FIG. 10 is a weld schedule showing another example of the disclosed multi-stage spot welding method; -
FIG. 11 is a weld schedule showing yet another example of the disclosed multi-stage spot welding method; -
FIG. 12 is a weld schedule showing still another example of the disclosed multi-stage spot welding method; and -
FIG. 13 is a weld schedule showing still another example of the disclosed multi-stage spot welding method. - Spot-welding a steel workpiece and an aluminum-based workpiece (aluminum or aluminum alloys) presents some notable challenges, as discussed above. The surface oxide layer(s) present on the aluminum-based workpiece are difficult to breakdown and disintegrate, which, during traditional spot welding techniques, leads to weld defects at the faying interface in the form of micro-cracks and other disparities caused by residual oxides. Moreover, the steel workpiece is more thermally and electrically resistive than the aluminum-based workpiece, meaning that the steel workpiece acts as a heat source and the aluminum-based workpiece acts as a heat conductor. The resultant thermal gradient established between the workpieces during and just after electrical current flow has a tendency to drive gas porosity and other disparities in the molten weld pool, including the residual oxide defects, towards and along the faying interface, and also contributes to the formation and growth of brittle Fe—Al intermetallic compounds at the faying interface in the form of one or more thin reaction layers on the steel workpiece. A multi-stage spot welding method has been devised that counterbalances these challenges and improves the ability to successfully and repeatedly spot weld steel and aluminum-based workpieces together.
- The multi-stage spot welding method invokes control of the electrical current passed between opposed welding electrodes and through the steel and aluminum-based workpieces in order to carry out multiple stages of weld joint development. The multiple stages include: (1) a molten weld pool growth stage in which a molten weld pool is initiated and grown within the aluminum-based workpiece; (2) a molten weld pool solidification stage in which the molten weld pool is allowed to cool and solidify into a weld nugget that forms all or part of a weld joint (the weld joint may also include intermetallic compound layers); (3) a weld nugget re-melting stage in which at least a portion of the weld nugget is re-melted; (4) a re-melted weld nugget solidification stage in which the re-melted portion of the weld nugget is allowed to cool and solidify; and optionally (5) a metal expulsion stage in which at least part of the re-melted portion of the weld nugget is expelled along the faying interface of the workpieces. The several stages of the disclosed method, in particular the weld nugget re-melting stage (stage 3), function to diminish the adverse effects of, and at least partially eradicate, the weld defects in the weld nugget that are believed to weaken the weld joint. The multi-stage spot welding method thus enhances the strength, especially the peel strength, of the ultimately-formed weld joint that gets put into service.
-
FIGS. 1-7 illustrate exemplary embodiments of the multi-stage spot welding method as performed on a workpiece stack-up 10 by aweld gun 18 that is mechanically and electrically configured to execute spot welding practices in accordance with a programmed weld schedule. The workpiece stack-up 10 includes at least asteel workpiece 12 and an aluminum-basedworkpiece 14. As shown here inFIGS. 1-2 , for example, the workpiece stack-up 10 may include only the steel and aluminum-basedworkpieces up 10, despite not being shown here, such as an additional steel workpiece or an additional aluminum-based workpiece. The term “workpiece” and its steel and aluminum-based variations is used broadly in the present disclosure to refer to a sheet metal layer, a casting, an extrusion, or any other piece that is resistance spot weldable, inclusive of any surface layers or coatings, if present. - The
steel workpiece 12 may be coated or uncoated steel. Such workpieces include galvanized (zinc-coated) low carbon steel, low carbon bare steel, galvanized advanced high strength steel (AHSS), and hot-stamped boron steel. Some specific types of steels that may be used in thesteel workpiece 12 are interstitial-free (IF) steel, dual-phase (DP) steel, transformation-induced plasticity (TRIP) steel, high-strength low alloy (HSLA) steel, and press-hardened steel (PHS). Regarding the aluminum-basedworkpiece 14, it may coated or uncoated aluminum or aluminum alloy. Aluminum alloys contain 85 wt. % or more aluminum—such as 5XXX, 6XXX, and 7XXX series aluminum alloys—and can be employed in a variety of tempers. Several types of aluminum alloys that may be employed include an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy, or an aluminum-zinc alloy, any of which may be coated with zinc or a conversion coating to improve adhesive bond performance, if desired. Some specific aluminum alloys that may be used in the aluminum-basedworkpiece 14 are AA5754 and AA5182 aluminum-magnesium alloy, AA6111 and AA6022 aluminum-magnesium-silicon alloy, and AA7003 and 7055 aluminum-zinc alloy. - The steel and aluminum-based
workpieces predetermined weld site 16 by theweld gun 18. When stacked-up for spot welding, thesteel workpiece 12 includes afaying surface 20 and anexterior surface 22. Likewise, the aluminum-basedworkpiece 14 includes afaying surface 24 and anexterior surface 26. The faying surfaces 20, 24 of the twoworkpieces faying interface 28 at theweld site 16. Thefaying interface 28, as used herein, encompasses instances of direct contact between the faying surfaces 20, 24 of theworkpieces workpieces workpieces thickness weld site 16. Thethicknesses workpieces - The
weld gun 18 is shown schematically inFIG. 1 and is one part of a larger automated welding operation within a manufacturing setting. Theweld gun 18, for example, may be mounted on a robot positioned in the vicinity of a conveyor or other transport device that is set up to deliver the workpiece stack-up 10 (as well as others like it and others unlike it) to theweld gun 18. The robot may be constructed to move theweld gun 18 along the workpiece stack-up 10, once delivered, so that a rapid succession of spot welds can be formed at manydifferent weld sites 16. Theweld gun 18 may also be a stationary pedestal-type weld gun in which the workpiece stack-up 10 is manipulated and moved relative to theweld gun 18 to enable the formation of multiple spot welds atdifferent weld sites 16 around the stack-up 10. Theweld gun 18 is, of course, meant to represent other types and arrangements of weld guns not specifically mentioned or described here so long as they are capable of spot welding the workpiece stack-up 10 according to the prescribed multi-step spot welding method. - The
weld gun 18 includes afirst gun arm 30 and asecond gun arm 32 that are mechanically and electrically configured to repeatedly form spot welds in accordance with a defined weld schedule. Thefirst gun arm 30 has afirst electrode holder 34 that retains a firstspot welding electrode 36, and thesecond gun arm 32 has asecond electrode holder 38 that retains a secondspot welding electrode 40. The first and secondspot welding electrodes - The first
spot welding electrode 36 includes afirst weld face 42 and the secondspot welding electrode 40 includes asecond weld face 44. The weld faces 42, 44 of the first and secondspot welding electrodes electrodes exterior surfaces workpieces spot welding electrode electrodes gun arms electrode holders spot welding electrodes - The first and second
spot welding electrodes weld face spot welding electrode weld face spot welding electrodes - The
welding gun arms spot welding electrodes up 10. Here, as shown inFIGS. 1-2 , the opposite sides of the workpiece stack-up 10 are the oppositely-facing exterior surfaces 22, 26 of the overlapping steel and aluminum-basedworkpieces second gun arms first gun arm 30 is moveable along its longitudinal axis towards thesecond gun arm 32 by anactuator 46 such as an air cylinder or a servo motor. Anactuator control 48 may cause compressed air to be delivered to theactuator 46, if theactuator 46 is an air cylinder, or it may cause current/voltage to be delivered to theactuator 46, if theactuator 46 is a servo motor, to move thefirst gun arm 30 as intended to press the weld faces 42, 44 against opposite sides of the workpiece stack-up 10 (surfaces 22, 26) and to apply the desired clamping force. The first and second weld faces 42, 44 are typically pressed against their respective exterior surfaces 22, 26 in diametric alignment with one another at theweld site 16. - The
weld gun 18 is also configured to pass electrical current between the first and secondspot welding electrodes up 10 at theweld site 16—when the weld faces 42, 44 of theelectrodes up 10. Electrical current can be delivered to theweld gun 18 from acontrollable power supply 50. Thepower supply 50 is preferably a medium-frequency DC (MFDC) power supply that electrically communicates with thespot welding electrodes - The
power supply 50 is controlled by aweld controller 52 in accordance with a programmed weld schedule. Theweld controller 52, which cooperates with the actuator control 48 (by means not shown), interfaces with thepower supply 50 and sets the applied current level, duration, and current type (constant, pulsed, etc.) of electrical current being passed between thespot welding electrodes weld controller 52 instructs thepower supply 50 to deliver electrical current such that the various stages of weld joint development called for in the multi-stage spot welding method are accomplished. The stages of the multi-stage spot welding method, as mentioned above, include (1) the molten weld pool growth stage, (2) the molten weld pool solidification stage, (3) the weld nugget re-melting stage, (4) the re-melted weld nugget solidification stage, and optionally (5) the metal expulsion stage, each of which will be explained in more detail below. - Referring now to
FIGS. 3-7 , the multi-stage spot welding method, including its various stages of weld joint development, is illustrated in general schematic fashion. To begin, the workpiece stack-up 10 is located between the first and secondspot welding electrodes weld site 16 is generally aligned with the opposed weld faces 42, 44. The workpiece stack-up 10 may be brought to such a location, as is often the case when thegun arms gun arms electrodes weld site 16. Once the stack-up 10 is properly located, the first andsecond gun arms spot welding electrodes up 10 at theweld site 16, which, in this embodiment, are the oppositely-facing exterior surfaces 22, 26 of the steel and aluminum-basedworkpieces FIG. 3 . Upon making contact with the workpiece stack-up 10 under pressure, the first and second weld faces 42, 44 impress into their respective opposite side surfaces of the stack-up 10. The resultant indentations originated by the opposed weld faces 42, 44 are referred to here as afirst contact patch 54 and asecond contact patch 56. - The molten weld pool growth stage is commenced once the
spot welding electrodes up 10 at theweld site 16. During the molten weld pool growth stage, amolten weld pool 58 is initiated and grown within the aluminum-basedworkpiece 14, as schematically depicted inFIG. 3 . Themolten weld pool 58 extends from thefaying interface 28 of theworkpieces workpiece 14. And it is composed predominantly of molten aluminum-based material from the aluminum-basedworkpiece 14 since thesteel workpiece 12 typically does not melt. Themolten weld pool 58 may penetrate a distance into the aluminum-basedworkpiece 14 that ranges from 20% to 100% (i.e., all the way through the aluminum-based workpiece 14) of thethickness 140 of the aluminum-basedworkpiece 14 at theweld site 16. Thethickness 140 of the aluminum-basedworkpiece 14 at theweld site 16 is typically less than the thickness outside of theweld site 16 due to the indentation of thesecond contact patch 56 on the workpiece stack-up 10. The portion of themolten weld pool 58 adjacent to thefaying interface 28, consequently, wets thefaying surface 20 of thesteel workpiece 12. - The
molten weld pool 58 is initiated and grown by passing electrical current between thespot welding electrodes workpieces faying interface 28 for a first period of time. Resistance to the flow of the electrical current through theworkpieces faying interface 28 generates heat and initially heats up thesteel workpiece 12 more quickly than the aluminum-basedworkpiece 14. The generated heat eventually initiates themolten weld pool 58 and then continues to grow themolten weld pool 58 to its desired size. Indeed, at the beginning of electrical current flow when thesecond contact patch 56 is smallest in area and current density is highest, themolten weld pool 58 initiates quickly and rapidly grows and penetrates into the aluminum-basedworkpiece 14. As thesecond contact patch 56 formed by the weld face 44 of the secondspot welding electrode 40 increases in area over the course of electrical current flow, the electrical current density decreases and themolten weld pool 58 grows more laterally in the vicinity of thefaying interface 28. - When carrying out the molten weld pool growth stage, the level of the applied electrical current and the duration of the first period of time depend on several factors. The main factors that influence the electrical current level and duration are the
thicknesses workpieces weld site 16 and the exact compositions of theworkpieces - After the molten weld pool has been initiated and grown, the molten weld pool solidification stage is carried out. During the molten weld pool solidification stage, the
molten weld pool 58 is allowed to cool and solidify into aweld nugget 60 that forms all or part of a weld joint 62, as illustrated inFIG. 4 . Cooling and solidification of themolten weld pool 58 can be realized over a second period of time in one of two ways. First, passage of electrical current between the first and secondspot welding electrodes spot welding electrodes weld pool 58, thus allowing themolten weld pool 58 to cool and solidify, albeit at a slower rate than ceasing electrical current flow entirely. Again, like before, the duration of the second period of time and the reduced current level (which allows solidification to happen) may vary depending on thethicknesses workpieces weld site 16 and the actual compositions of theworkpieces molten weld pool 58 into theweld nugget 60. - The
weld nugget 60 extends a distance from thefaying interface 28 into the aluminum-basedworkpiece 14 to apenetration depth 64. Thepenetration depth 64 of theweld nugget 60 may range from 20% to 100% (i.e., all the way through the aluminum-based workpiece 14) of thethickness 140 of the aluminum-basedworkpiece 14 at theweld site 16. Thethickness 140 of the aluminum-basedworkpiece 14 at theweld site 16, as before, is typically less than the thickness outside of theweld site 16 due to the indentation of thesecond contact patch 56 on the workpiece stack-up 10. Additionally, theweld nugget 60 defines aweld bond area 66, as shown inFIG. 7 , which is the surface area of theweld nugget 60 adjacent with and joined to thefaying surface 20 of thesteel workpiece 12 by way of intervening intermetallic Fe—Al reaction layers. Theweld bond area 66, as reported in mm2, is preferably at least 4(π)(t) in which “t” is thethickness 140 of the aluminum-basedworkpiece 14 in millimeters at theweld site 16 prior to origination of thesecond contact patch 56. In other words, when calculating the preferred 4(π)(t) weld bond area, the thickness “t” of the aluminum-basedworkpiece 14 is the original thickness of theworkpiece 14 as measured prior to indentation of the weld face 44 of the secondspot welding electrode 40. Theweld bond area 66 can be varied as desired by managing the size of themolten weld pool 58 grown in the molten weld pool growth stage. - The
weld nugget 60 may include weld defects dispersed at and along thefaying interface 28 within theweld bond area 66. These defects—which can include gas porosity, shrinkage voids, micro-cracking, and surface oxide residue—are believed to be swept towards the fayinginterface 28 during solidification of themolten weld pool 58 where they have a tendency weaken the strength of the weld joint 62, in particular the peel strength, as previously explained. The weld joint 62 may also include, in addition to theweld nugget 60, one or more thin reaction layers of Fe—Al intermetallic compounds (not shown) on thesteel workpiece 12 and adjacent to thefaying interface 28, as previously indicated. These layers are produced mainly as a result of reaction between themolten weld pool 58 and thesteel workpiece 12 at spot welding temperatures. The one or more layers of Fe—Al intermetallic compounds may include intermetallics such as FeAl3, Fe2Al5, as well others, and their combined thickness typically ranges from 1 μm to 10 μm. The hard and brittle nature of the Fe—Al intermetallic compounds is also thought to negatively affect the strength of the overall weld joint 62. - After the weld joint 62 has been established, the weld nugget re-melting stage is performed. During the weld nugget re-melting stage, at least a
portion 68 of theweld nugget 60 is re-melted, as depicted inFIG. 5 . There-melted portion 68 of theweld nugget 60 preferably includes at least part of theweld bond area 66 that was established during the molten weld pool solidification stage. It also typically does not extend all the way to thepenetration depth 64 of theweld nugget 60. The shallower penetration of there-melted portion 68 occurs because at the time of the weld nugget re-melting stage, the weld face 44 of the secondspot welding electrode 40 has indented further into the workpiece stack-up 10, and thesecond contact patch 56 has correspondingly increased in size, meaning that electrical current is passed between thespot welding electrodes faying interface 28 with less penetration into the aluminum-basedworkpiece 14. There-melted portion 68 of theweld nugget 60, moreover, may be entirely confined within theweld bond area 66 or it may encompass the entireweld bond area 66 and actually combine with freshly melted material from the aluminum-basedworkpiece 14 outside of, and adjacent to, theweld bond area 66 to established an enlarged weld bond area 70 (FIG. 7 ). The area of the enlargedweld bond area 70, if created, may be up to 50% greater than theweld bond area 66 of theweld nugget 60 before re-melting. - The
weld nugget 60 is at least partially re-melted by passing electrical current between thespot welding electrodes workpieces spot welding electrode 40 is further impressed into the workpiece stack-up 10 and thefaying interface 28 is less liable to generate heat within theweld site 16 since the weld joint 62 is more electrically conductive than the distinct,unjoined faying surfaces workpieces thicknesses workpieces weld site 16 and the exact compositions of theworkpieces - The electrical current delivered during the weld nugget re-melting stage is preferably in the form of current pulses that may or may not increase in applied current level over the course of the third period of time. Like before, when pulsed, the passing electrical current is a plurality of current pulses delivered over the third period of time. Each current pulse may last from 10 ms to 200 ms and have a peak current level between, for example, 15 kA and 50 kA, with periods of zero current flow lasting from, for example, 1 ms to 100 ms between pulses. The current pulses can be said to increase in applied current level when at least 75% of the current pulses, and preferably 100%, attain a peak current level that is greater than the peak current level of the immediately preceding current pulse. The use of current pulses may be practiced in the weld nugget re-melting stage for several reasons. Most notably, the use of current pulses helps prevent excessive penetration of the
re-melted portion 68 of theweld nugget 60 by keeping the electrode/workpiece cool, which also has the benefit of preserving the operational lifetime of the secondspot welding electrode 40. - The re-melting of the
weld nugget 60 is believed to positively impact the strength, including the peel strength, of the ultimately-formed weld joint 62 that is placed into service. Without being bound by theory, it is believed that re-melting theweld nugget 60, especially theweld bond area 66 at thefaying interface 28, cleans out the various weld defects that get driven to and along thefaying interface 28 during solidification of themolten weld pool 58, thus improving the ability of theweld nugget 60 to bond with thefaying surface 20 of thesteel workpiece 12. The creation of there-melted portion 68, for example, is thought to consolidate entrained gas porosity near the center of theweld nugget 62, and possibly evolve some gas from there-melted portion 68, while thermal expansion and contraction of theweld nugget 60 during re-melting is thought to break up and disperse residual oxides and micro-cracks that may be present at theweld bond area 66 or in the vicinity. - Following the weld nugget re-melting stage, the re-melted weld nugget solidification stage is performed. During the re-melted weld nugget solidification stage, the
re-melted portion 68 of the weld nugget 60 (as well as any newly melted material of the aluminum-basedworkpiece 14 outside of the original weld bond area 66) is allowed to cool and solidify, as shown inFIG. 6 , preferably with the first and secondspot welding electrodes up 10. There-solidified portion 72 of theweld nugget 60, which is derived from there-melted portion 68, is depicted here as a distinct part of theweld nugget 60 although, in actual practice, there-solidified portion 72 may not be easily distinguishable from the part(s) of the weld nugget 60 (if any) that do not undergo re-melting and re-solidification. And, as alluded to above, there-solidified portion 72 of theweld nugget 60 is believed to contain less weld defects at or near thefaying interface 28 than would otherwise be present had the weld nugget re-melting stage not been practiced. To be sure, it is not uncommon for workpiece stack-ups that have undergone the multi-stage spot welding method to have peel strengths of at least 100% greater than the same workpiece stack-ups that have been spot welded with a conventional single-step constant current. - The multi-stage spot welding method set forth above may also include an optional metal expulsion stage during or after the weld nugget re-melting stage but prior to the re-melted weld nugget solidification stage. During the metal expulsion stage, at least part of the
re-melted portion 68 of theweld nugget 60 is heated to the extent that the hydraulic seal established at theweld site 16 is broken, resulting in the faying surfaces 20, 24 of the steel and aluminum-basedworkpieces spot welding electrodes 36, 40). There-melted portion 68 of theweld nugget 60, and possibly some of the newly melted material of the aluminum-basedworkpiece 14 outside of the originalweld bond area 66, if present, expels or spatters laterally along thefaying interface 28 outside of theweld bond area 66 at this time until the workpieces eventually collapse 12, 14 due to the loss of molten material and the applied pressure of the first and secondspot welding electrodes weld nugget 60 of weld defects by physically expelling the defects outside of the weld bond area 66 (or the enlargedweld bond area 70 if applicable). While metal expulsion is deemed beneficial, the heating of there-melted portion 68 is preferably controlled so that thethickness 140 of the aluminum-basedworkpiece 14 at theweld site 16 is not reduced to less than 50% of its original thickness, which is measured prior to indentation of the weld face 44 of the secondspot welding electrode 40, as a result of the metal expulsion stage. - The metal expulsion stage can be accomplished by passing electrical current between the
spot welding electrodes workpieces thicknesses workpieces - After the multi-stage spot welding method has resulted in the formation of the weld joint 62, including the
weld nugget 60 having there-solidified portion 72, the first and secondspot welding electrodes respective contact patches up 10 is then successively located relative to theweld gun 18 atother weld sites 16, and the multi-stage spot welding process is repeated at thosesites 16, or the workpiece stack-up 10 is moved away from theweld gun 18 to make way for another stack-up. The above-described multi-stage spot welding method can thus be carried out many times at different weld sites on the same workpiece stack-up as well as different workpiece stack-ups in a manufacturing setting to successfully, consistently, and reliably form weld joints between a steel workpiece and an aluminum-based workpiece. - The following examples demonstrate several embodiments of the disclosed multi-stage spot welding method. The weld schedule of a conventional spot welding method that employs a single step constant electrical current to weld a 1.2-mm 6022 aluminum alloy workpiece to a 1.0-mm hot-dip galvanized low carbon steel workpiece is also illustrated in
FIG. 8 for comparative purposes. There, as can be seen, electrical current is passed between the spot welding electrodes and through the workpiece stack-up at a constant current level (after a rapid initial ramp up) of 16 kA for 500 ms under 800 lb of force. In contrast, as described below in Examples 1-5 and illustrated inFIGS. 9-13 , spot weld joints are formed by controlling passage of electrical current between the spot welding electrodes and through the workpiece stack-ups in order to carry out, in order, a molten weld pool growth stage, a molten weld pool solidification stage, a weld nugget re-melting stage, and a re-melted weld nugget solidification stage. Each of the examples, moreover, employs an optional metal expulsion stage before the re-melted weld nugget solidification stage. - Here, in the first example, a 1.2-mm 6022 aluminum alloy workpiece was spot welded to a 1.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 800 lb of force applied by the spot welding electrodes. The weld schedule is depicted in
FIG. 9 . As shown, electrical current at a constant level of 17 kA was first passed through the workpieces for a first period of 125 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece. Next, passage of electrical current was ceased, i.e., dropped to 0 kA, for a second period of 500 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces. Electrical current was then re-started and passed through the workpieces to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface of the workpieces. The electrical current passed at that time had a constant current level of 25 kA and was maintained for a third period of 200 ms. After the third period of time, passage of electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget. - In this example, which is depicted in
FIG. 10 , a 1.2-mm 6022 aluminum alloy workpiece was spot welded to a 1.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 700 lb of force applied by the spot welding electrodes. As shown, electrical current at a constant current level of 15 kA was passed through the workpieces for a first period of 300 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece. Next, passage of electrical current was ceased for a second period of 500 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces. Electrical current was then passed in the form of seven current pulses to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface of the workpieces. The seven current pulses increased in applied current level in the range of 16 kA to 20.5 kA over a third period of approximately 860 ms. Specifically, each current pulse lasted for 100 ms while increasing in current level, then dropped to 0 kA for a period of 25 ms between pulses, and the peak current levels of each pulse increased from its immediately succeeding pulse (16.5 kA<17.2 kA<17.8 kA<18.5 kA<19.1 kA<19.8 kA<20.4 kA). After the seventh and last current pulse, passage of the electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget. - In this example, which is depicted in
FIG. 11 , a 2.0-mm 6022 aluminum alloy workpiece was spot welded to a 1.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 800 lb of force applied by the spot welding electrodes. Here, as shown, electrical current at a constant current level of 17 kA was passed through the workpieces for a first period of 125 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece. Next, passage of electrical current was ceased for a second period of 500 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces. Electrical current was then passed in the form of twenty seven current pulses over a third period of approximately 960 ms to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface. Each current pulse reached a current level of 37 kA and maintained that level for 12 ms before dropping to 0 kA for a period of 24 ms between pulses. After the twenty-seventh and last current pulse, passage of the electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget. - In this example, which is depicted in
FIG. 12 , a 1.2-mm 6022 aluminum alloy workpiece was spot welded to a 2.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 600 lb of force applied by the spot welding electrodes. Here, electrical current at a constant level of 13 kA was passed through the workpieces for a first period of 250 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece. Next, passage of electrical current was ceased for a second period of 500 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces. Electrical current was then passed in the form of eight current pulses over a third period of approximately 910 ms to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface. Specifically, each current pulse reached a current level of 14 kA and maintained that level for 100 ms before dropping to 0 kA for a period of 15 ms between pulses. After the eighth and last current pulse, passage of the electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget. - In this example, which is depicted in
FIG. 13 , a 2.0-mm 6022 aluminum alloy workpiece was spot welded to a 2.0-mm hot-dip galvanized low carbon steel workpiece by the multi-stage spot welding method under 1200 lb of force applied by the spot welding electrodes. To begin, as shown, electrical current was passed in the form of 20 current pulses over a first period of approximately 400 ms to initiate and grow a molten weld pool within the aluminum alloy workpiece. Each current pulse reached a current level of 20 kA and maintained that level for 16 ms before dropping to 0 kA for a period of 4 ms between pulses. Next, passage of electrical current was ceased for a second period of 1000 ms to solidify the molten weld pool into a weld nugget, which along with one or more Fe—Al intermetallic layers formed a weld joint between the steel and aluminum alloy workpieces. Electrical current was then passed in the form of twelve current pulses over a third period of approximately 480 ms to re-melt at least a portion of the weld nugget and, additionally, to cause metal expulsion at the faying interface. Each current pulse reached a current level of 38 kA and maintained that level for 16 ms before dropping to 0 kA for a period of 25 ms between pulses. After the twelfth and last current pulse, passage of the electrical current was again ceased while the force of the electrodes was maintained to solidify the re-melted portion of the weld nugget. - The following table compares the peel strengths of the conventional single-step constant electrical current welding method (
FIG. 8 ) to the five exemplary multi-step spot welding methods (FIGS. 9-13 ). Weld joint peel strength is noteworthy property for weld joints. This is especially true for weld joints used in conjunction with a structural adhesive since adhesives generally provide shear strength, but perform poorly in peel. The peel strengths reported here were measured with T-peel samples. The T-peel samples were obtained by first bending coupons (5 in. by 1.5 in.) into an L-shape. The short legs of two L-shape coupons were then mated and a weld joint was formed according to the above detailed spot welding methods between the mating surfaces. The long legs of the resultant T-peel samples were mounted in a tensile machine and the pulled until the weld joint failed. Maximum loading in Newtons (N) is reported as the peel strength. As can be seen, the peel strengths obtained from the multi-stage spot welding methods were significantly greater than the peel strength obtained from the conventional single-step spot welding method. -
COMPARISON OF PEEL STRENGTHS Spot Welding Method Peel Strength (N) Conventional (FIG. 8) 90 Multi-Step (FIG. 9) 220 Multi-Step (FIG. 10) 290 Multi-Step (FIG. 11) 260 Multi-Step (FIG. 12) 400 Multi-Step (FIG. 13) 810 - The above description of preferred exemplary embodiments and specific examples are merely descriptive in nature; they are not intended to limit the scope of the claims that follow. Each of the terms used in the appended claims should be given its ordinary and customary meaning unless specifically and unambiguously stated otherwise in the specification.
Claims (20)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US15/976,163 US10981243B2 (en) | 2013-08-23 | 2018-05-10 | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US201361869281P | 2013-08-23 | 2013-08-23 | |
US14/464,476 US9999938B2 (en) | 2013-08-23 | 2014-08-20 | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
US15/976,163 US10981243B2 (en) | 2013-08-23 | 2018-05-10 | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US14/464,476 Continuation US9999938B2 (en) | 2013-08-23 | 2014-08-20 | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
Publications (2)
Publication Number | Publication Date |
---|---|
US20180257166A1 true US20180257166A1 (en) | 2018-09-13 |
US10981243B2 US10981243B2 (en) | 2021-04-20 |
Family
ID=52479432
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US14/464,476 Active 2037-03-13 US9999938B2 (en) | 2013-08-23 | 2014-08-20 | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
US15/976,163 Active 2035-08-13 US10981243B2 (en) | 2013-08-23 | 2018-05-10 | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US14/464,476 Active 2037-03-13 US9999938B2 (en) | 2013-08-23 | 2014-08-20 | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
Country Status (2)
Country | Link |
---|---|
US (2) | US9999938B2 (en) |
CN (1) | CN104668756B (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US10625367B2 (en) * | 2016-04-08 | 2020-04-21 | GM Global Technology Operations LLC | Method of resistance spot welding aluminum to steel |
US11326680B2 (en) | 2019-10-17 | 2022-05-10 | GM Global Technology Operations LLC | High strength joints between steel and titanium |
US11772184B2 (en) | 2018-09-13 | 2023-10-03 | Arcelormittal | Welding method for the manufacture of an assembly of at least 2 metallic substrates |
US11919102B2 (en) | 2018-09-13 | 2024-03-05 | Arcelormittal | Assembly of at least 2 metallic substrates |
Families Citing this family (34)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE112013005619T5 (en) * | 2012-11-22 | 2015-08-27 | Kabushiki Kaisha F.C.C. | Process for producing a joined element and a joined element |
US20160082543A1 (en) * | 2013-06-05 | 2016-03-24 | Nippon Steel & Sumitomo Metal Corporation | Spot-welded joint and spot welding method |
US20150001885A1 (en) * | 2013-06-28 | 2015-01-01 | GM Global Technology Operations LLC | Mixed material underbody for noise controlled occupant compartment |
US9999938B2 (en) | 2013-08-23 | 2018-06-19 | GM Global Technology Operations LLC | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
US10166627B2 (en) | 2013-10-04 | 2019-01-01 | GM Global Technology Operations LLC | Aluminum alloy to steel welding process |
US10010966B2 (en) | 2014-02-14 | 2018-07-03 | GM Global Technology Operations LLC | Electrode for resistance spot welding of dissimilar metals |
JP2016055337A (en) * | 2014-09-11 | 2016-04-21 | 高周波熱錬株式会社 | Welding method and welded structure |
US9999939B2 (en) | 2014-12-05 | 2018-06-19 | GM Global Technology Operations LLC | Resistance spot welding steel and aluminum workpieces with electrode insert |
US10376984B2 (en) | 2015-03-30 | 2019-08-13 | GM Global Technology Operations LLC | Conical shaped current flow to facilitate dissimilar metal spot welding |
US10252369B2 (en) | 2015-07-07 | 2019-04-09 | GM Global Technology Operations LLC | Cooling to control thermal stress and solidification for welding of dissimilar materials |
US10272515B2 (en) * | 2015-09-15 | 2019-04-30 | GM Global Technology Operations LLC | Power pulse method for controlling resistance weld nugget growth and properties during steel spot welding |
US10245675B2 (en) | 2015-10-14 | 2019-04-02 | GM Global Technology Operations LLC | Multi-stage resistance spot welding method for workpiece stack-up having adjacent steel and aluminum workpieces |
US10675702B2 (en) | 2016-02-16 | 2020-06-09 | GM Global Technology Operations LLC | Joining of light metal alloy workpieces to steel workpieces using resistance spot welding and adhesive |
US10766095B2 (en) | 2016-03-01 | 2020-09-08 | GM Global Technology Operations LLC | Mating electrodes for resistance spot welding of aluminum workpieces to steel workpieces |
US10500679B2 (en) | 2016-03-30 | 2019-12-10 | GM Global Technology Operations LLC | Resistance welding electrode and method of resistance welding |
US10981244B2 (en) | 2016-03-30 | 2021-04-20 | GM Global Technology Operations LLC | Resistance welding electrode |
US10751830B2 (en) | 2016-04-08 | 2020-08-25 | GM Global Technology Operations LLC | Welding electrode for use in a resistance spot welding workpiece stack-ups that include an aluminum workpiece and a steel workpiece |
US10675703B2 (en) | 2016-04-08 | 2020-06-09 | GM Global Technology Operations LLC | Al-steel weld joint |
US10857619B2 (en) | 2016-04-14 | 2020-12-08 | GM Global Technology Operations LLC | Control of intermetallic compound growth in aluminum to steel resistance welding |
US10682724B2 (en) | 2016-04-19 | 2020-06-16 | GM Global Technology Operations LLC | Resistance spot welding of aluminum-to-aluminum, aluminum-to-steel, and steel-to-steel in a specified sequence and using a cover |
US10675704B2 (en) | 2016-04-22 | 2020-06-09 | GM Global Technology Operations LLC | Alternately direct resistance spot welding of Al-to-Al, al-to-steel, and steel-to-steel with welding electrode having oxide-disrupting structural features |
US10421148B2 (en) | 2016-04-25 | 2019-09-24 | GM Global Technology Operations LLC | External heat assisted welding of dissimilar metal workpieces |
DE102017113120A1 (en) | 2016-06-16 | 2017-12-21 | GM Global Technology Operations LLC | Multi-stage geometry of the welding side of an electrode for joining aluminum and steel by welding |
CA3041124C (en) * | 2016-10-21 | 2021-03-23 | Novelis Inc. | Enhanced resistance spot welding using cladded aluminum alloys |
US10730133B2 (en) | 2017-11-08 | 2020-08-04 | GM Global Technology Operations LLC | Electrode weld face design |
JP6981275B2 (en) | 2018-01-24 | 2021-12-15 | トヨタ自動車株式会社 | How to join dissimilar metal plates |
JP6984469B2 (en) * | 2018-02-09 | 2021-12-22 | トヨタ自動車株式会社 | How to join dissimilar metal plates |
JP7010720B2 (en) * | 2018-02-13 | 2022-01-26 | トヨタ自動車株式会社 | Resistance spot welding method |
US10857618B2 (en) | 2018-02-28 | 2020-12-08 | GM Global Technology Operations LLC | Improving mechanical performance of Al-steel weld joints by limiting steel sheet deformation |
US11065710B2 (en) | 2018-03-14 | 2021-07-20 | GM Global Technology Operations LLC | Resistance spot welding workpiece stack-ups having a steel workpiece and an aluminum workpiece with a steel plate |
JP6963282B2 (en) * | 2018-04-20 | 2021-11-05 | 株式会社神戸製鋼所 | Aluminum material resistance spot welding joints and aluminum material resistance spot welding method |
CN110814499A (en) * | 2019-09-26 | 2020-02-21 | 安徽巨一自动化装备有限公司 | Method for reducing grinding frequency of aluminum alloy spot welding electrode |
CN112570867B (en) * | 2019-09-27 | 2023-02-14 | 中国科学院上海光学精密机械研究所 | Method for inhibiting internal defects of resistance spot welding nuggets of aluminum alloy |
CN115446437B (en) * | 2022-09-14 | 2023-11-10 | 首钢集团有限公司 | Resistance spot welding method, device, equipment and storage medium |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2011224578A (en) * | 2010-04-15 | 2011-11-10 | Kobe Steel Ltd | Method for joining dissimilar materials |
JP2013151017A (en) * | 2011-12-27 | 2013-08-08 | Mazda Motor Corp | Welding method |
Family Cites Families (53)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5302797A (en) | 1991-08-30 | 1994-04-12 | Sumitomo Metal Industries, Ltd. | Resistance welding of aluminum |
US5783794A (en) | 1993-11-15 | 1998-07-21 | Nippon Steel Corporation | Method and material for resistance welding steel-base metal sheet to aluminum-base metal sheet |
WO1997010920A1 (en) | 1995-09-18 | 1997-03-27 | Honda Giken Kogyo Kabushiki Kaisha | Method of lap joining two kinds of metallic members having different melting points |
JPH11342477A (en) | 1998-06-01 | 1999-12-14 | Mitsubishi Electric Corp | Spot welding method |
JP4303629B2 (en) | 2004-04-02 | 2009-07-29 | 本田技研工業株式会社 | Resistance welding method of different materials, aluminum alloy material, and resistance welding member of different materials |
JP4519508B2 (en) | 2004-04-21 | 2010-08-04 | 株式会社神戸製鋼所 | Dissimilar joints of steel and aluminum |
US7951465B2 (en) * | 2004-04-21 | 2011-05-31 | Kobe Steel, Ltd. | Joined body of dissimilar materials comprising steel material and aluminum material, and joining method therefor |
US7126077B2 (en) | 2004-05-10 | 2006-10-24 | General Motors Corporation | Resistance welding of high strength steels |
US7850059B2 (en) | 2004-12-24 | 2010-12-14 | Nissan Motor Co., Ltd. | Dissimilar metal joining method |
JP4868210B2 (en) | 2005-12-06 | 2012-02-01 | 日産自動車株式会社 | Bonding method of dissimilar materials |
CN102114574B (en) | 2006-02-23 | 2013-01-09 | 株式会社神户制钢所 | Joint product between steel product and aluminum material, spot welding method, and electrode chip for use in the method |
US8927894B2 (en) | 2006-09-28 | 2015-01-06 | GM Global Technology Operations LLC | Weld electrode for attractive weld appearance |
US8058584B2 (en) | 2007-03-30 | 2011-11-15 | Nissan Motor Co., Ltd. | Bonding method of dissimilar materials made from metals and bonding structure thereof |
JP5468350B2 (en) * | 2009-10-23 | 2014-04-09 | マツダ株式会社 | Dissimilar metal plate joining method |
US8274010B2 (en) * | 2010-04-28 | 2012-09-25 | GM Global Technology Operations LLC | Welding electrode with contoured face |
US9676065B2 (en) | 2010-04-28 | 2017-06-13 | GM Global Technology Operations LLC | Resistance spot welding of aluminum to aluminum and steel to steel |
JP5333560B2 (en) | 2011-10-18 | 2013-11-06 | Jfeスチール株式会社 | Resistance spot welding method and resistance spot welding joint of high strength steel plate |
US20130189023A1 (en) | 2011-12-21 | 2013-07-25 | Alcoa Inc. | Apparatus and methods for joining dissimilar materials |
US8991030B2 (en) | 2012-04-06 | 2015-03-31 | GM Global Technology Operations LLC | Forming method for projection welding projections |
US9987705B2 (en) | 2013-06-07 | 2018-06-05 | GM Global Technology Operations LLC | Resistance spot welding of steel to pre-coated aluminum |
US9999938B2 (en) | 2013-08-23 | 2018-06-19 | GM Global Technology Operations LLC | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece |
US10052710B2 (en) | 2013-08-23 | 2018-08-21 | GM Global Technology Operations LLC | Resistance spot welding steel and aluminum workpieces using electrode weld face cover |
US9839971B2 (en) | 2013-09-20 | 2017-12-12 | GM Global Technology Operations LLC | Resistance spot welding steel and aluminum workpieces with hot welding electrode at aluminum workpiece |
US10058949B2 (en) | 2013-10-04 | 2018-08-28 | GM Global Technology Operations LLC | Resistance spot welding steel and aluminum workpieces using insertable cover |
US10166627B2 (en) | 2013-10-04 | 2019-01-01 | GM Global Technology Operations LLC | Aluminum alloy to steel welding process |
US10010966B2 (en) | 2014-02-14 | 2018-07-03 | GM Global Technology Operations LLC | Electrode for resistance spot welding of dissimilar metals |
US20150231730A1 (en) | 2014-02-17 | 2015-08-20 | GM Global Technology Operations LLC | Resistance spot welding steel and aluminum workpieces with protuberance |
US20150352658A1 (en) | 2014-06-10 | 2015-12-10 | GM Global Technology Operations LLC | Intruding feature in aluminum alloy workpiece to improve al-steel spot welding |
US20150352659A1 (en) | 2014-06-10 | 2015-12-10 | GM Global Technology Operations LLC | Cover plate with intruding feature to improve al-steel spot welding |
US10279418B2 (en) | 2014-07-16 | 2019-05-07 | Honda Motor Co., Ltd. | Method and apparatus for resistive spot welding |
US9999939B2 (en) | 2014-12-05 | 2018-06-19 | GM Global Technology Operations LLC | Resistance spot welding steel and aluminum workpieces with electrode insert |
US10259071B2 (en) | 2015-03-27 | 2019-04-16 | GM Global Technology Operations LLC | Resistive welding electrode and method for spot welding steel and aluminum alloy workpieces with the resistive welding electrode |
US10376984B2 (en) | 2015-03-30 | 2019-08-13 | GM Global Technology Operations LLC | Conical shaped current flow to facilitate dissimilar metal spot welding |
US20160346865A1 (en) | 2015-05-27 | 2016-12-01 | GM Global Technology Operations LLC | Resistance spot welding workpiece stack-ups of different combinations of steel workpieces and aluminum workpieces |
US10252369B2 (en) | 2015-07-07 | 2019-04-09 | GM Global Technology Operations LLC | Cooling to control thermal stress and solidification for welding of dissimilar materials |
US10245675B2 (en) | 2015-10-14 | 2019-04-02 | GM Global Technology Operations LLC | Multi-stage resistance spot welding method for workpiece stack-up having adjacent steel and aluminum workpieces |
US20170157697A1 (en) | 2015-12-08 | 2017-06-08 | GM Global Technology Operations LLC | Welding electrode for use in resistance spot welding workpiece stack-ups that include an aluminum workpiece and a steel workpiece |
US10610956B2 (en) | 2016-02-04 | 2020-04-07 | GM Global Technology Operations LLC | Welding electrode cutting tool and method of using the same |
US10456856B2 (en) | 2016-02-04 | 2019-10-29 | GM Global Technology Operations LLC | Welding electrode cutting tool and method of using the same |
US10675702B2 (en) | 2016-02-16 | 2020-06-09 | GM Global Technology Operations LLC | Joining of light metal alloy workpieces to steel workpieces using resistance spot welding and adhesive |
US10766095B2 (en) | 2016-03-01 | 2020-09-08 | GM Global Technology Operations LLC | Mating electrodes for resistance spot welding of aluminum workpieces to steel workpieces |
US10500679B2 (en) | 2016-03-30 | 2019-12-10 | GM Global Technology Operations LLC | Resistance welding electrode and method of resistance welding |
US10675703B2 (en) | 2016-04-08 | 2020-06-09 | GM Global Technology Operations LLC | Al-steel weld joint |
US10625367B2 (en) | 2016-04-08 | 2020-04-21 | GM Global Technology Operations LLC | Method of resistance spot welding aluminum to steel |
US10751830B2 (en) | 2016-04-08 | 2020-08-25 | GM Global Technology Operations LLC | Welding electrode for use in a resistance spot welding workpiece stack-ups that include an aluminum workpiece and a steel workpiece |
US10682723B2 (en) | 2016-04-13 | 2020-06-16 | GM Global Technology Operations LLC | Resistance spot welding steel and aluminum workpieces with electrode having insert |
US10857619B2 (en) | 2016-04-14 | 2020-12-08 | GM Global Technology Operations LLC | Control of intermetallic compound growth in aluminum to steel resistance welding |
US10682724B2 (en) | 2016-04-19 | 2020-06-16 | GM Global Technology Operations LLC | Resistance spot welding of aluminum-to-aluminum, aluminum-to-steel, and steel-to-steel in a specified sequence and using a cover |
US20170297134A1 (en) | 2016-04-19 | 2017-10-19 | GM Global Technology Operations LLC | Resistance spot welding aluminum to steel using preplaced metallurgical additives |
US20170297137A1 (en) | 2016-04-19 | 2017-10-19 | GM Global Technology Operations LLC | Method of joining aluminum and steel workpieces |
US10675704B2 (en) | 2016-04-22 | 2020-06-09 | GM Global Technology Operations LLC | Alternately direct resistance spot welding of Al-to-Al, al-to-steel, and steel-to-steel with welding electrode having oxide-disrupting structural features |
US10421148B2 (en) | 2016-04-25 | 2019-09-24 | GM Global Technology Operations LLC | External heat assisted welding of dissimilar metal workpieces |
US20170361392A1 (en) | 2016-06-16 | 2017-12-21 | GM Global Technology Operations LLC | Multistep electrode weld face geometry for weld bonding aluminum to steel |
-
2014
- 2014-08-20 US US14/464,476 patent/US9999938B2/en active Active
- 2014-08-23 CN CN201410849083.1A patent/CN104668756B/en active Active
-
2018
- 2018-05-10 US US15/976,163 patent/US10981243B2/en active Active
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2011224578A (en) * | 2010-04-15 | 2011-11-10 | Kobe Steel Ltd | Method for joining dissimilar materials |
JP2013151017A (en) * | 2011-12-27 | 2013-08-08 | Mazda Motor Corp | Welding method |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US10625367B2 (en) * | 2016-04-08 | 2020-04-21 | GM Global Technology Operations LLC | Method of resistance spot welding aluminum to steel |
US11772184B2 (en) | 2018-09-13 | 2023-10-03 | Arcelormittal | Welding method for the manufacture of an assembly of at least 2 metallic substrates |
US11919102B2 (en) | 2018-09-13 | 2024-03-05 | Arcelormittal | Assembly of at least 2 metallic substrates |
US11326680B2 (en) | 2019-10-17 | 2022-05-10 | GM Global Technology Operations LLC | High strength joints between steel and titanium |
Also Published As
Publication number | Publication date |
---|---|
CN104668756B (en) | 2018-09-21 |
US9999938B2 (en) | 2018-06-19 |
US20150053655A1 (en) | 2015-02-26 |
CN104668756A (en) | 2015-06-03 |
US10981243B2 (en) | 2021-04-20 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US10981243B2 (en) | Multi-step direct welding of an aluminum-based workpiece to a steel workpiece | |
US10252369B2 (en) | Cooling to control thermal stress and solidification for welding of dissimilar materials | |
US10245675B2 (en) | Multi-stage resistance spot welding method for workpiece stack-up having adjacent steel and aluminum workpieces | |
US11123816B2 (en) | Aluminum alloy to steel welding process | |
US10259071B2 (en) | Resistive welding electrode and method for spot welding steel and aluminum alloy workpieces with the resistive welding electrode | |
US10376984B2 (en) | Conical shaped current flow to facilitate dissimilar metal spot welding | |
US11084119B2 (en) | Electrode for resistance spot welding of dissimilar materials | |
US10625367B2 (en) | Method of resistance spot welding aluminum to steel | |
US20150352658A1 (en) | Intruding feature in aluminum alloy workpiece to improve al-steel spot welding | |
US20150352659A1 (en) | Cover plate with intruding feature to improve al-steel spot welding | |
US10682723B2 (en) | Resistance spot welding steel and aluminum workpieces with electrode having insert | |
US20150231730A1 (en) | Resistance spot welding steel and aluminum workpieces with protuberance | |
US20170157697A1 (en) | Welding electrode for use in resistance spot welding workpiece stack-ups that include an aluminum workpiece and a steel workpiece | |
US20170297137A1 (en) | Method of joining aluminum and steel workpieces | |
US20170361392A1 (en) | Multistep electrode weld face geometry for weld bonding aluminum to steel | |
US10751830B2 (en) | Welding electrode for use in a resistance spot welding workpiece stack-ups that include an aluminum workpiece and a steel workpiece | |
US10272515B2 (en) | Power pulse method for controlling resistance weld nugget growth and properties during steel spot welding | |
US10240222B2 (en) | Current schedule for optimized reaction metallurgical joining | |
JP4656495B2 (en) | Joining method and joining structure of oxide film forming material | |
CN111136372B (en) | High aspect ratio weld face design for dissimilar metal welding | |
US20200114459A1 (en) | Quality welding of similar and dissimilar metal welds with space between workpieces | |
DE102014112028A1 (en) | Multi-stage direct welding of an aluminum-based workpiece to a steel workpiece | |
CN110270750B (en) | Resistance spot welding workpiece stack comprising a steel workpiece and an aluminum workpiece having a steel plate | |
US20190134737A1 (en) | Aluminum to steel braze resistance spot welding | |
JP7360610B2 (en) | Spot welding method |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: GM GLOBAL TECHNOLOGY OPERATIONS LLC, MICHIGAN Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SIGLER, DAVID R.;CARLSON, BLAIR E.;MYASNIKOVA, YELENA;AND OTHERS;SIGNING DATES FROM 20140912 TO 20140916;REEL/FRAME:045768/0252 |
|
FEPP | Fee payment procedure |
Free format text: ENTITY STATUS SET TO UNDISCOUNTED (ORIGINAL EVENT CODE: BIG.); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY |
|
STPP | Information on status: patent application and granting procedure in general |
Free format text: DOCKETED NEW CASE - READY FOR EXAMINATION |
|
STPP | Information on status: patent application and granting procedure in general |
Free format text: NON FINAL ACTION MAILED |
|
STPP | Information on status: patent application and granting procedure in general |
Free format text: FINAL REJECTION MAILED |
|
STPP | Information on status: patent application and granting procedure in general |
Free format text: RESPONSE AFTER FINAL ACTION FORWARDED TO EXAMINER |
|
STPP | Information on status: patent application and granting procedure in general |
Free format text: PUBLICATIONS -- ISSUE FEE PAYMENT RECEIVED |
|
STPP | Information on status: patent application and granting procedure in general |
Free format text: PUBLICATIONS -- ISSUE FEE PAYMENT VERIFIED Free format text: AWAITING TC RESP, ISSUE FEE PAYMENT VERIFIED |
|
STPP | Information on status: patent application and granting procedure in general |
Free format text: PUBLICATIONS -- ISSUE FEE PAYMENT VERIFIED |
|
STCF | Information on status: patent grant |
Free format text: PATENTED CASE |